The invention relates generally to a color-printing machine and more specifically, to a color printing machine employing dye diffusion electrography.
Dye sublimation based marking systems are emerging as real contenders in the high quality color printer marketplace. Existing commercial products typically use a thermal printhead to selectively sublime dyes from donor ribbons into a polymer coated receiving sheet. This process which has been named Dye Diffusion Thermal Transfer, hereinafter (D2T2), produces near photographic quality prints and transparencies due in part to the color purity and color mixing properties of dyes.
In the process, a thermal head is used to transfer dye from a color ribbon onto a receiver paper. The thermal head consist of a number of resistive elements deposited by a thin film process onto an alumina substrate and arranged in a linear array. Each approximately square element is split at right angles to the direction of the array (in order to minimize visible structure in the print), and is independently addressable by virtue of multiple input lines and logic circuitry on the head. Printing is carried out by energizing the head with data corresponding to the image while driving a color ribbon and receiver paper under the head, thus writing the entire image during a single pass. The quantity of dye transferred, and thus the intensity of color generated at each image point, is controlled by the temperature at the ribbon/receiver interface. By adjusting the on-time of each element in the head during printing, a continuous tone image is produced. Full color is achieved by overprinting entire fields of the three subtractive primary colors: yellow, magenta, and cyan.
There are several disadvantages with D2T2, including slow process speed, cost per copy, and security. The process speed of D2T2 is limited due to achievable dye diffusion rates which creates high energy demands on the thermal printhead. The cost per copy is high because of the consumption of dye coated donor ribbons and the special polymer coated paper requirement. In addition to posing a potential security xe2x80x9cleakxe2x80x9d because they retain mirror images of printed material, used donor films present the user of D2T2 systems with the problem of dye-film disposal in our increasingly sensitive xe2x80x9cever greenxe2x80x9d environment.
In response to these problems, a need exists for an alternative color printing process that can retain the high quality dye coloration advantages of D2T2, while achieving a significant reduction in problems associated therewith.
The following disclosure may be relevant to some aspect of the present invention.
In U.S. Pat. No. 3,900,318 to Zographos et al., a process is disclosed which involved the use of sublimable dispersed dyes in photoelectrophoretic image reproduction. The dispersed dyes can be converted into the vapor phase at temperatures of between 160xc2x0 and 220xc2x0 C under atmospheric pressure. In this imaging process, the dye-containing particles themselves are the photoreceptors.
U.S. Pat. No. 4,251,611 to Mehl et al., discloses a process for the information of a permanent image in which one or more colors from a latent electrostatic image which correspond to the color separations of an original are developed by means of a developer composed of polymer particles containing a dyestuff which can sublime or polymer particles containing a dyestuff which can sublime or vaporize at between 100xc2x0 and 250xc2x0C. Latent images are developed on a photoconducting element by means of a developer containing, in addition to the dyestuff, a ferromagnetic substance incorporated into the polymer particles. Each image thus developed is brought into contact with a receiving sheet which possesses an affinity for the vapors of the sublimable or vaporizable dyestuff of the developers. Next, the resulting material is heated above the vaporization or sublimation temperature of the dyestuff to be transferred. These steps are carried out in the case of each latent image, until the image to be reproduced has been recomposed. This process can effectively destroy the photoreceptor and is not suitable for use in a plain paper xerographic application.
U.S. Pat. No. 4,262,078 to Ishida et al., discloses a light transmitting particle containing a sublimable color-former which is a pyridine derivative suitable for use in the formation of a color image. The process of Ishida et al. uses the light transmitting characteristics of the particle to form an image.
U.S. Pat. No. 4,238,562 to Ishida et al., discloses a light transmission particle for forming a color image. The particle contains a sublimable dye that is a spirobenzopyran indole compound suitable for use in the formation of a color image. The process disclosed in Ishida et al. is similar to that of U.S. Pat. No. 4,262,078, in that the process uses the light transmitting characteristics of the particle to form the image.
U.S. Pat. No. 4,230,784, issued to Nishiguchi et al., discloses imageforming particles for use in electrostatic image production. These particles have a light transmitting property and comprise an electrically conductive material and a subliming substance. In the process of Nishiguchi et al., an image is formed by directly exposing tile toner.
U.S. Pat. No. 4,124,384 to Centa, discloses an image reproduction process is disclosed which uses a photohardenable element containing photohardenable layers toned with a toner material comprising a sublimable dye. The process involves heating the above-stated toned layer while in contact with a receptor material, therefore causing the dye to sublime imagewise and condense on the receptor material. The receptor comprises polymer organic compounds.
U.S. Pat. No. 4,456,669 to Yubakami et al., discloses an image forming process disclosed utilizing heat-transferable dyes to form images on a receiving substrate. Images signals are used to arrange image forming particles on a support member. The particles contain a dye former which is heat-transferred onto an image receiving substrate. After heating, a color developing agent is used to adhere to the dye former to provide colored images.
U.S. Pat. No. 4,121,932 to Ishida, discloses an electrophotographic process for forming a dye image. The process comprises an electrophotographic material containing a photoconductive layer consisting of photoconductive powders and sublimable dyes. The electrophotographic process further comprises charging a photosensitive element consisting of photoconductive particles and sublimable dyes, exposing and developing the element with acidic toners, heating the element to sublime the dyes and transferring the dye images to an accepting substrate.
In accordance with an aspect of the invention there is provided a printing machine for producing an image on a recording sheet, including means for recording an electrostatic latent image on the recording sheet; means for developing the electrostatic latent image with donor particles carrying sublimable dye marking material of a first color to form a developed image pattern on the recording sheet; means for subliming a dye image pattern conforming to the developed image pattern into the recording sheet; and a recovery system for picking up said donor material from the recording sheet.
In accordance with another aspect of the invention there is provided a printing machine for producing an image on a recording sheet, including: an ionic projection writing head for recording an electrostatic latent image the recording sheet; a developer unit having donor material carrying a sublimable dye marking particles of a first color therein for developing the electrostatic latent image on the recording sheet; a heater for subliming the developed image onto the recording sheet; and a recovery system for picking up said donor material from the recording sheet.
In accordance with another aspect of the invention there is provided a method for producing an image on a recording sheet, including the steps of: recording an electrostatic latent image on the recording sheet; developing the electrostatic latent image with donor material carrying a sublimable dye of a first color to form a developed image on the recording sheet; and subliming dye from the developed image into the recording sheet.
An advantageous effect of the present invention is that the quantity of dye materials and donor material used is proportional to the actual coloration required rather than the full-page quantity of dyes consumed per print as in the Dye Diffusion Thermal Transfer process. Also, the particulate nature of donor particles and recovery thereof will scramble the mirror image thereby resolving any security issues.